This invention relates to a voltage detector for detecting different voltage levels in conductors of an electrical power line and generating corresponding acoustic or optical warning signals.
Prior art electric voltage detectors usually are provided with a contact element or feeder destined either to be placed in contact with, or to the brought in proximity of a conductor which might be alive. Such apparatus comprises its own source of voltage which is connected to a warning device by the intermediary of a detecting circuit provided with semiconductors which are capable of letting pass or interrupting the current of said source when a feeler is subjected to a potential which at least is equal to a predetermined value constituting the threshold sensitivity. When this threshold is attained the detection circuit is converted to conductive condition and lets pass the current of said source to the warning device which then emits a signal, for example an acoustic signal, indicating the presence of a voltage. Such detectors usually comprise an auxiliary circuit permitting to apply at the input of the detector circuit a voltage equivalent to that which reaches it in the actual conditions of use and which allows to check its good condition of operation.
The state of the art is illustrated in the German Pat. Nos. 1,134,157 and 1,054,169, the Austrian Pat. No. 288,544, the Swiss Pat. No. 492,222.
Such apparatus is principally used for ascertaining whether the conductors of a line or of an installation are insulated with respect to their source of energy and whether it is thus possible to ground and short-circuit them, and then to effect work on them. Nevertheless, even in this case, these conductors have a residual voltage induced by other adjacent conductors which remained connected to the power line. When this voltage, though being relatively weak, still exceeds the threshold of sensitivity of the detector, this latter emits a signal of presence of voltage and it becomes impossible to discriminate these conductors under induced voltage from those fed by direct voltage. However, it is advisable that the operator becomes aware of the presence of an induced voltage.
The object of the present invention is the provision of a detector which is capable of emitting signals, preferably acoustic signals, of at least two different kinds of which can be easily distinguished and which are released respectively from at least two thresholds of different voltages applied to the feeler. If these thresholds are conveniently spaced with respect to the voltage of the power line, such a detector will emit a certain signal in presence of a conductor under direct voltage, and a different signal in presence of a conductor only under an induced residual voltage.
If such a detector comprises more than two thresholds of different voltage conveniently spaced and a corresponding number of kinds of signals will be emitted, it could be used in a great number of installations having voltages of different magnitudes and would allow, for all of them to obtain a different signal according to the installation being energized by direct voltage or by an induced residual voltage.
In practice, the signal emitted by most of the known detectors is not absolutely invariable and can be influenced in a certain degree by the potential which is applied to the feeler. For example, it is the case of a luminous signal which becomes more brilliant when this potential increases, or still the case of a musical note which varies more or less (in intensity, in frequency, etc.) according to the potential, but it is impossible to interpret these variations in order to evaluate at least approximately the magnitude of the potential applied to the feeler.
The primary object of the invention accordingly is a voltage detector capable of emitting signals of different form which can be easily recognized, corresponding each to a determined threshold potential. For example, when the three thresholds of increasing potentials are designated by P1, P2 and P3, the warning device will emit, from the threshold P1, a sequence of long and spaced acoustic signals. When the potential will attain the value P2 the signals will become short and approached. Finally, at a potential at least equal to P3, the apparatus will emit a uniform uninterrupted sound.
It will be understood that the warning device can emit optical signals, or there can be adopted continuous acoustic signals, but of different tonality, a variety of signals being easily available to the expert.